Media: comic? Manga? Anime? no to these Other visual media? yes Other textual media? no, but there have been textual media created about it Something else animated? It's a visual and audio medium, and there is a form of animation involved...

Disneyland? YUP Is it a rollercoaster ride? nope Is the cemetery an uncharacteristically morbid thing to include in this particular scenery? not at all, it's more that it was a pet cemetery and where it was Do any other scenery elements stand out? yes, but not relevant

Did you expect a cemetery for humans? YES Was the pet cemetery less scary? no Was it placed in an odd location? YES Was it a real pet cemetery? no, despite urban legend that a actual dog is buried under one of the tombstones Was it near the ride entrance? Exit? yes to both, it's near an area that is used both to enter and exit the ride Was it up in the air? no

You have most of this solved, it's a faux pet cemetery located in an out of the way place near an entrance/exit to the Haunted Mansion ride, but other than expecting that such a detail would be a cemetery for humans there is another reason you would not expect this pet cemetery to be there...

Anything near the cemetery relevant? yes Other scenery? yes Is there another copy of the same cemetery somewhere? no, but OTRT Is there something that makes the cemetery seem silly or otherwise less scary? no

Is it supposed to be hidden? not really hidden, but it's placement is intentional Is it redundant because most won't see it? no Can it be considered an easter egg? not really Does one have to do something special to be able to see it? no, there is a special condition that enables you to see it, but irrel You were on the right track when you asked if there was a duplicate of the cemetery...

At the Haunted Mansion in Disneyland there is a small pet cemetery on the west side of the Mansion facade. This west side is an area where most guests are not even normally allowed to go or can even really see from anywhere else. When I found out about this, I was surprised as there is a much larger, impossible to miss pet cemetery in front of the Mansion. That one is actually a new pet cemetery added later mainly because the original pet cemetery is so out of the way. The only people who saw the old one were cast members and wheelchair-bound guests and their families as it is next to a wheelchair accessible entrance to the ride. Plus, I thought just the idea of having any pet cemetery at the Mansion at all a bit morbid in a way a regular human cemetery would not necessarily be, but both PC's are actually done in good taste and humor.

Here is a great article that goes into more detail and history and includes some pictures. Note: the article says the urban legend is that a cat is really buried in the old "secret" cemetery, but everywhere else I have heard the UL says it's a dog.